This invention relates generally to a reservoir for holding liquids such as hydraulic fluids and, more specifically, to a reservoir having an end portion with a relatively large opening adapted to be mounted to, for example, a hydraulic manifold.
The invention is especially useful in a hydraulic power pack of the type having a hydraulic pump located inside the reservoir. In this instance, the open end portion of the reservoir is sized to fit over the pump prior to being secured to the manifold.
A generally cylindrical mounting ring is either joined to or integrally formed at the open end of the reservoir. The mounting ring is typically adapted to receive threaded fasteners for securing the reservoir to the manifold. An O-ring establishes a circumferential seal between the internal cylindrical surface of the mounting ring and an upwardly projecting cylindrical portion of the manifold to seal the open end of the reservoir.
Either plastic or steel reservoirs can be used for storing hydraulic fluid in a hydraulic power pack. Plastic reservoirs, however, offer several advantages over comparable steel reservoirs. Plastic reservoirs are relatively lightweight and will not corrode. In addition, plastic reservoirs can be made from a translucent material to permit a quick visual check of the level of oil in the reservoir. Despite these advantages, plastic reservoirs have not been widely accepted for use in prior hydraulic power packs.
The mounting ring of the reservoir is subjected to continuous forces that tend to expand the cylindrical portion of the mounting ring. Specifically, the radial squeeze on the O-ring causes an outwardly directed force on the cylindrical portion of the mounting ring. While this force is relatively low, over time, the continuous nature of the force caused by the O-ring, combined with the heating cycles experienced during normal operation of the power pack, will cause a mounting ring which has been made from a common plastic compound to relax and deform outwardly. In those instances where the reservoir is either above or horizontally level with the manifold, at least a portion of the mounting ring is subjected to additional outwardly acting forces due to hydrostatic pressure caused by the weight of the fluid in the reservoir. Eventually, relaxation of the mounting ring will result in failure of the circumferential seal and leakage of hydraulic fluid from the reservoir. For this reason, prior mounting rings are typically made from a metal having sufficient strength and stiffness to withstand the continuous forces of the open end of the reservoir.
Steel mounting rings are easily integrated with steel reservoirs. For example, a steel mounting ring can be welded to a steel body. Alternately, a steel mounting ring may be integrally formed at the open end portion of a steel reservoir. It is difficult, however, to secure a steel mounting ring to a plastic body without the use of an additional sealing arrangement between the body and the mounting ring. As a result of the need for a steel mounting ring and the difficulty in securing a steel mounting ring to a plastic body, prior reservoirs for power packs are typically made from steel or other suitable metal.